Methods of forming staircase-shaped connection structures of three-dimensional semiconductor devices

ABSTRACT

Provided is a staircase-shaped connection structure of a three-dimensional semiconductor device. The device includes an electrode structure on a substrate, the electrode structure including an upper staircase region, a lower staircase region, and a buffer region therebetween. The electrode structure includes horizontal electrodes sequentially stacked on the substrate, the horizontal electrodes include a plurality of pad regions constituting a staircase structure of each of the upper and lower staircase regions, and the buffer region has a width that is larger than that of each of the pad regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application is a continuation of U.S.patent application Ser. No. 15/910,583 filed Mar. 2, 2018, which is adivisional of U.S. patent application Ser. No. 15/249,903 filed Aug. 29,2016, now U.S. Pat. No. 9,941,122, which is a divisional of U.S. patentapplication Ser. No. 14/520,751 filed Oct. 22, 2014, now U.S. Pat. No.9,455,268, which claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2014-0016653 filed Feb. 13, 2014, in the KoreanIntellectual Property Office, the entire contents of which are herebyincorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Example embodiments of the inventive concepts relate tothree-dimensional semiconductor devices, and in particular, toconnection structures of three-dimensional semiconductor devices and amethods of forming the same.

In semiconductor devices, increased integration is an important factorin realizing high-performance low-cost devices. Currently, in atwo-dimensional memory semiconductor device or a planar memorysemiconductor device, integration is largely affected by a technique offorming a fine pattern, because integration is often determined by anarea that a unit memory cell occupies. However, since it may bedifficult and/or expensive to form a fine pattern, it may be difficultto continue to increase integration of a two-dimensional memorysemiconductor device.

To overcome such a limitation, three-dimensional memory devices (thatis, including three-dimensionally arranged memory cells) have beenproposed. Not only the memory cells but also interconnection lines(e.g., word lines or bit lines) are three-dimensionally arranged in thethree-dimensional memory devices.

SUMMARY

Example embodiments of the inventive concepts can provide a highlyreliable fabrication process capable of forming a staircase-shapedconnection structure.

Example embodiments of the inventive concepts can provide a simplifiedfabrication process capable of forming a staircase-shaped connectionstructure.

Example embodiments of the inventive concepts can provide asemiconductor device including electrodes with a staircase-shapedconnection structure.

According to example embodiments of the inventive concepts, athree-dimensional semiconductor device may include an electrodestructure on a substrate, the electrode structure including an upperstaircase region, a lower staircase region, and a buffer regiontherebetween. The electrode structure may include horizontal electrodessequentially stacked on the substrate, the horizontal electrodes mayinclude a plurality of pad regions constituting a staircase structure ofeach of the upper and lower staircase regions, and the buffer region mayhave a width that is larger than that of each of the pad regions.

In example embodiments, the buffer region may have a thickness that issmaller than or equal to a minimum thickness of the upper staircaseregion and is greater than or equal to a maximum thickness of the lowerstaircase region.

In example embodiments, the device may further include an insulatinglayer on, and in some embodiments covering, the electrode structure. Theinsulating layer may have a flat top surface and covers an entire topsurface of the buffer region.

In example embodiments, the insulating layer may have a substantiallymonotonically increasing thickness in a direction from the upperstaircase region to the lower staircase region.

In example embodiments, the buffer region may be in direct contact withthe insulating layer.

In example embodiments, the electrode structure further may include acell array region, the upper staircase region may be located between thecell array region and the lower staircase region, and the upper andlower staircase regions may have a stepwise-decreasing thickness in adirection away from the cell array region.

In example embodiments, each of the upper and lower staircase regionsmay have at least two different thicknesses, which are changed in analternating manner, when measured at a same distance from the cell arrayregion.

In example embodiments, when viewed in a plan view, an uppermost one ofthe horizontal electrodes constituting the buffer region may include aconnecting portion continuously extending from the upper staircaseregion to the lower staircase region, and a protruding portionhorizontally protruding from the connecting portion, the protrudingportion being spaced apart from at least one of the upper and lowerstaircase regions.

In example embodiments, when viewed in a plan view, an uppermost one ofthe horizontal electrodes constituting the buffer region may extend fromthe upper staircase region continuously to the lower staircase regionand may expose a second uppermost one of the horizontal electrodes fromthe upper staircase region continuously to the lower staircase region.

In example embodiments, the device may further includecharge-storing-type and/or variable-resistance-type memory cells thatmay be three-dimensionally arranged on the substrate.

According to other example embodiments of the inventive concepts, asemiconductor device may comprise a staircase on the substrate. Thestaircase comprises a plurality of steps having conductive treads and anintermediate landing. In some embodiments, the intermediate landing isdeeper than each of the conductive treads. Moreover, in some of theembodiments, the intermediate landing includes a conductive surface.Also, in some embodiments, at least one of the conductive treadsincludes multiple levels.

Other example embodiments may further comprise a plurality of conductivevias, a respective one of which electrically contacts a respective oneof the respective treads and extends away from the respective one of theconductive treads. Other embodiments may further comprise an insulatinglayer on the staircase. The insulating layer includes a flat outersurface on the steps, and a flat outer surface on the intermediatelanding. In still other embodiments, the insulating layer increases inthickness going down the steps of the staircase.

According to example embodiments of the inventive concepts, a method offabricating a three-dimensional semiconductor device may includesequentially stacking a plurality of horizontal layers on a substrate toform a stack, patterning some of the horizontal layers to form a firststaircase region with at least one first multi-level stair, patterningothers of the horizontal layers to form a second staircase region withat least one second multi-level stair, and patterning both of the firstand second staircase regions at once to form single-level stairs in eachof the first and second multi-level stairs. The first and secondstaircase regions may be formed in such a way that a distancetherebetween is larger than a width of each of the single-level stairstherein.

In example embodiments, the first and second multi-level stairs may beformed by at least one trimming process, and the trimming process mayinclude forming a mask pattern on, and in some embodiments to cover, thehorizontal layers, etching the horizontal layers to a multi-layer depthusing the mask pattern as an etch mask, etching the mask pattern toreduce an occupying area of the mask pattern, and etching the horizontallayers to a multi-layer depth using the etched mask pattern as an etchmask.

In example embodiments, the forming of the single-level stairs mayinclude forming a photoresist layer on, and in some embodiments tocover, the first and second staircase regions, performing aphotolithography process to form a photoresist pattern, in which atleast one opening is formed across the first and second multi-levelstairs, etching the stack to a single-layer depth using the photoresistpattern as an etch mask, and removing the photoresist pattern.

In example embodiments, the photolithography process may includeexposing the first and second staircase regions at once, and the openingmay be formed to continuously cross both of the first and secondstaircase regions.

In example embodiments, the photolithography process may include firstand second exposure steps, which are performed to expose the first andsecond staircase regions, respectively.

In example embodiments, the first and second exposure steps may beperformed using different process conditions of focal length.

In example embodiments, the at least one opening includes a firstopening crossing the first staircase region, and a second openingcrossing the second staircase region. The first and second openings maybe formed spaced apart from each other between the first and secondstaircase regions.

In example embodiments, the stack may further include a cell arrayregion, the first staircase region may be formed between the cell arrayregion and the second staircase region, and each of the first and secondstaircase regions may have a stepwise-decreasing thickness in adirection away from the cell array region.

In example embodiments, the method may further include forming verticalpatterns penetrating the stack, and forming a memory layer between thevertical patterns and the horizontal layers. The memory layer mayinclude a layer capable of realizing a charge-storing-type and/orvariable-resistance-type memory element.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingbrief description taken in conjunction with the accompanying drawings.The accompanying drawings represent non-limiting, example embodiments asdescribed herein.

FIGS. 1-5, 6A, 6B, 7-11, 12A and 12B are perspective views illustratinga method of forming a staircase-shaped connection structure according toexample embodiments of the inventive concepts.

FIGS. 13 and 14 are perspective views illustrating a method of forming astaircase-shaped connection structure according to other exampleembodiments of the inventive concepts.

FIG. 15 is a sectional view illustrating a coated profile of aphotoresist layer according to a comparative example.

FIG. 16 is a graph showing a change in thickness of a photoresist layerwith respect to position in the comparative example.

FIG. 17 is a sectional view illustrating a coated profile of aphotoresist layer according to example embodiments of the inventiveconcepts.

FIG. 18 is a graph showing a change in thickness of a photoresist layerwith respect to position example embodiments of the inventive concepts.

FIG. 19 is a sectional view illustrating a coated profile of aphotoresist layer according to other example embodiments of theinventive concepts.

FIG. 20 is a graph showing a change in thickness of a photoresist layerwith respect to position according to other example embodiments of theinventive concepts.

FIG. 21 is a circuit diagram illustrating a three-dimensionalsemiconductor memory device according to example embodiments of theinventive concepts.

FIGS. 22 through 25 are sectional views illustrating portions ofthree-dimensional semiconductor memory devices according to exampleembodiments of the inventive concepts.

FIG. 26 is a circuit diagram illustrating a three-dimensionalsemiconductor memory device according to other example embodiments ofthe inventive concepts.

FIGS. 27 and 28 are schematic block diagrams illustrating electronicdevices including a semiconductor device according to exampleembodiments of the inventive concepts.

It should be noted that these figures are intended to illustrate thegeneral characteristics of methods, structures and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. These drawings are not, however, to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment, and should not be interpreted as defining orlimiting the range of values or properties encompassed by exampleembodiments. For example, the relative thicknesses and positioning ofmolecules, layers, regions and/or structural elements may be reduced orexaggerated for clarity. The use of similar or identical referencenumbers in the various drawings is intended to indicate the presence ofa similar or identical element or feature.

DETAILED DESCRIPTION

Example embodiments of the inventive concepts will now be described morefully with reference to the accompanying drawings, in which exampleembodiments are shown. Example embodiments of the inventive conceptsmay, however, be embodied in many different forms and should not beconstrued as being limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the concepts of example embodimentsto those of ordinary skill in the art. In the drawings, the thicknessesof layers and regions are exaggerated for clarity. Like referencenumerals in the drawings denote like elements, and thus theirdescription will be omitted.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements or layers should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” “on” versus “directly on”). As used herein the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes” and/or “including,” if usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Example embodiments of the inventive concepts are described herein withreference to cross-sectional illustrations that are schematicillustrations of idealized embodiments (and intermediate structures) ofexample embodiments. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, example embodiments of theinventive concepts should not be construed as limited to the particularshapes of regions illustrated herein but are to include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle may have rounded or curvedfeatures and/or a gradient of implant concentration at its edges ratherthan a binary change from implanted to non-implanted region. Likewise, aburied region formed by implantation may result in some implantation inthe region between the buried region and the surface through which theimplantation takes place. Thus, the regions illustrated in the figuresare schematic in nature and their shapes are not intended to illustratethe actual shape of a region of a device and are not intended to limitthe scope of example embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments of theinventive concepts belong. It will be further understood that terms,such as those defined in commonly-used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

FIGS. 1-5, 6A, 6B, 7-11, 12A and 12B are perspective views illustratinga method of forming a staircase-shaped connection structure according toexample embodiments of the inventive concepts.

Referring to FIG. 1, a stack 110 may be formed on a substrate 100. Inexample embodiments, the substrate 100 may include a layer having asemiconductor property. For example, the substrate 100 may be asemiconductor wafer or a multi-layered structure including at least onesemiconductor layer, but example embodiments of the inventive conceptsare not limited thereto.

The stack 110 and/or the substrate 100 may include a cell array regionCAR, an upper staircase region USR, a buffer region BFR, and a lowerstaircase region LSR. The upper staircase region USR may be locatedbetween the cell array region CAR and the lower staircase regions LSR,and the buffer region BFR may be located between the upper and lowerstaircase regions USR and LSR.

The stack 110 may include a plurality of interlayered insulating layers112 and a plurality of horizontal layers 114 alternatingly stacked onthe substrate 100. The horizontal layers 114 may be formed of a materialhaving an etch selectivity with respect to the interlayered insulatinglayers 112. For example, each of the interlayered insulating layers 112may be a silicon oxide layer, and each of the horizontal layers 114 mayinclude at least one of a silicon nitride layer, a silicon oxynitridelayer, a poly silicon layer, or metal layers.

In order to reduce complexity in the drawings, the stack 110 includingtwenty four horizontal layers 114 is illustrated in FIGS. 1 through 12B,but example embodiments of the inventive concepts are not limitedthereto and the number of the horizontal layers 114 constituting thestack 110 may range from 32 to 128. For example, the number of thehorizontal layers 114 constituting the stack 110 may range from 4 to1024.

The stack 110 may be patterned to form an upper staircase structure USSincluding multi-level stairs, which is provided in the upper staircaseregion USR of the stack 110. In example embodiments, the upper staircasestructure USS may be formed by a trimming process. For example, as shownin FIGS. 2 and 3, the trimming process may include forming a first maskpattern M1 on the stack 110, performing a first etching step using thefirst mask pattern M1 as an etch mask, etching the first mask pattern M1to form a trimmed first mask pattern tM1, and performing a secondetching step re-using the trimmed first mask pattern tM1 as an etchmask. The first mask pattern M1 may be or include a photoresist layer.

In example embodiments, the first and second etching steps may beperformed to etch several layers of the horizontal layers 114. Forexample, an etch depth in each of the first and second etching steps maybe greater than two times a vertical pitch of each of the horizontallayers 114. Accordingly, the stairs constituting the upper staircasestructure USS may be formed to have a height difference that is greaterthan two times the vertical pitch of each of the horizontal layers 114.This etching method may be referred to as a “multi-layer etching method”below.

If the first mask pattern M1 has a first width W1 at an initial stage,as the result of the etching of the first mask pattern M1, the trimmedfirst mask pattern tM1 may have a second width W2 that is smaller thanthe first width W1. In other words, the trimmed first mask pattern tM1may have a smaller occupied area than the first mask pattern M1. Forexample, the first mask pattern M1 may be formed to cover the cell arrayregion CAR and the upper staircase region USR and expose the bufferregion BFR and the lower staircase region LSR, and the trimmed firstmask pattern tM1 may be formed to cover the cell array region CAR and aportion of the upper staircase region USR and expose the remainingportion of the upper staircase region USR, the buffer region BFR, andthe lower staircase region LSR.

Accordingly, the trimmed first mask pattern tM1 may be formed to exposeone of the horizontal layers 114, which is newly exposed by the firstetching step, as well as another one of the horizontal layers 114, whichhas been covered with the first mask pattern M1 during the first etchingstep. This means that, during the first and second etching steps, anetching step is twice performed on a portion exposed by the first maskpattern M1 and is once performed on another portion newly exposed by thetrimmed first mask pattern tM1. As a result, as shown in FIG. 3, twostairs may be formed in the upper staircase region USR of the stack 110.

In order to reduce complexity in the drawings and to provide betterunderstanding of example embodiments of the inventive concepts, anexample of example embodiments, in which the trimming process includestwo etching steps, is illustrated in FIGS. 2 and 3. However, in certainembodiments, during the trimming process, the first mask pattern M1 maybe etched three times or more and then re-used in three or more etchingsteps.

Thereafter, as shown in FIG. 4, the trimming process may be repeatedlyperformed at least once to form the upper staircase structure USS in theupper staircase region USR of the stack 110.

Referring to FIGS. 5 and 6A, a lower staircase structure LSS may beformed in the lower staircase region LSR of the stack 110. Similar tothe upper staircase structure USS, the lower staircase structure LSS maybe formed by performing the trimming process on the lower staircaseregion LSR of the stack 110 at least once. For example, the formation ofthe lower staircase structure LSS may include forming a second maskpattern M2 to cover the cell array region CAR, the upper staircaseregion USR, the buffer region BFR, and the lower staircase region LSR,and re-using the second mask pattern M2 as an etch mask. Here, thesecond mask pattern M2 may be or include a photoresist layer.

The lower staircase structure LSS may be formed apart from the upperstaircase structure USS with the buffer region BFR interposedtherebetween. For example, a distance between the lower and upperstaircase structures LSS and USS or a width of the buffer region BFR maybe greater than a width of each of the multi-level stairs, which areformed in each of the lower and upper staircase structures LSS and USS.In example embodiments, the width of the buffer region BFR may be 3 to150 times the width of each of the multi-level stairs. The upper andlower staircase structures USS and LSS may be formed to have astepwise-decreasing thickness in a direction away from the cell arrayregion CAR, as shown in FIG. 6A.

FIG. 6B corresponds to FIG. 6A, but uses conventional terminology for astaircase. As is well known, a stairway or staircase is a constructiondesigned to bridge a large vertical distance by dividing it into smallervertical distance called steps. A step includes a tread and a riser. Thetread is the part of the stairway that is stepped on. The tread depth ismeasured from the outer edge of the step to the vertical riser betweensteps. The width is measured from one side to the other. A riser is thevertical portion between each tread on the stair. A landing or platformis an area of a floor near the top or bottom step of a stair. Anintermediate landing is a platform that is built as part of the stair.Thus, as illustrated in FIG. 6B, a semiconductor device according tovarious embodiments of the inventive concepts includes a staircase SC ona substrate 100. The staircase SC comprises a plurality of steps Shaving conductive treads T. The staircase SC also comprises anintermediate landing IL. As illustrated in FIG. 6B, the intermediatelanding IL is deeper than each of the conductive treads T. Theintermediate landing IL may include a conductive surface.

Next, as shown in FIG. 7, a third mask layer ML may be formed to coverthe stack 110 provided with the upper and lower staircase structures USSand LSS. The third mask layer ML may be a photoresist layer formedusing, for example, a spin-coating technique. As will be described belowin more detail with reference to FIGS. 15 through 20, the third masklayer ML may be formed to have a position-dependent varying thickness,because the stack 110 is formed to have the lower and upper staircasestructures LSS and USS. However, according to some example embodimentsof the inventive concepts, the variation in thickness of the third masklayer ML may be reduced or prevented due to the presence of the bufferregion BFR.

Referring to FIGS. 8 and 9, a photolithography process may be performedon the third mask layer ML to form a third mask pattern M3 with openingsOP. The openings OP may be formed to partially expose the upper andlower staircase structures USS and LSS. In some example embodiments, theformation of the third mask pattern M3 may include two exposure steps,which may be successively performed on the third mask layer ML, and onedeveloping step.

For example, one of the exposure steps may be performed to exposeportions of the third mask layer ML that are located on the lowerstaircase structure LSS and thus, as shown in FIG. 8, first exposedregions ER may be formed in a portion of the third mask layer ML locatedon the lower staircase structure LSS. Each of the first exposed regionsER may be formed across the lower staircase structure LSS and mayinclude a portion overlapping the buffer region BFR.

The other one of the exposure steps may be performed to expose otherportions of the third mask layer ML that are located on the upperstaircase structure USS, and thus, second exposed regions (not shown)may be formed in the other portions of the third mask layer ML locatedon the upper staircase structure USS. Each of the second exposed regionsmay be formed across the upper staircase structure and may include aportion overlapping the buffer region BFR. There may be differences inprocess conditions, such as a focal length, between the exposure stepsfor forming the first and second exposed regions. For example, theexposed regions (e.g., the first exposed regions ER) on the lowerstaircase region LSR may be formed under process conditions in which afocal length is longer than in a process for forming the exposed regions(e.g., the second exposed regions) on the upper staircase region USR.

The first exposed regions ER may be formed spaced apart from the secondexposed regions, with the buffer region BFR interposed therebetween.Accordingly, when the developing step is finished, the third maskpattern M3 may have the openings OP spaced apart from each other withthe buffer region BFR interposed therebetween, as shown in FIG. 9.

Next, as shown in FIG. 10, the horizontal layers 114 exposed by theopenings OP may be etched by a third etching step using the third maskpattern M3 as an etch mask. When it comes to an etch depth, the thirdetching step may be performed to etch one of the horizontal layers 114.For example, the etch depth of the third etching step may besubstantially equal to or smaller than a vertical pitch of each of thehorizontal layers 114. Accordingly, at least one single-level stair maybe formed in each of the multi-level stairs constituting the upper andlower staircase structures USS and LS S. This etching method may bereferred to as a “single-layer etching method” below.

The third mask pattern M3 may be removed. As shown in FIG. 11, the stack110 may be formed to have pads P1-P24 having respectively differentvertical and horizontal positions. Thereafter, additional processesrequired for fabricating a three-dimensional memory semiconductor devicemay be further performed on the stack 110 with the staircase-shapedconnection structure.

For example, as shown in FIG. 12A, an insulating layer 120 may be formedto cover the stack 110, cutting regions may be formed across the stack110, and then, vertical patterns may be formed to penetrate the stack110. The vertical patterns will be described below in more detail withreference to FIGS. 22 through 25. Thereafter, contact plugs 130 may beformed on the upper and lower staircase regions USR and LSR, and upperinterconnection lines may be connected to the contact plugs 130. Thecontact plugs 130 may be respectively connected to the horizontal layers114, which are separated from each other by the cutting regions. In someexample embodiments, before the formation of the contact plugs 130, thehorizontal layers 114 may be replaced with a conductive material througha replacement process. In this case, the contact plugs 130 may berespectively connected to conductive patterns, which are formed in placeof the horizontal layers 114.

As shown in FIG. 12A, a three-dimensional semiconductor device accordingto example embodiments of the inventive concepts may include theelectrode structure 110 provided on the substrate 100. The electrodestructure 110 may include horizontal electrodes sequentially stacked onthe substrate 100, when viewed in a section view, and may include theupper staircase region USR, the lower staircase region LSR, and thebuffer region BFR therebetween, when viewed in a plan view. Thehorizontal electrodes may have a plurality of pad regions (for example,P1 to P24 of FIG. 11), which constitute a staircase structure in each ofthe upper and lower staircase regions USR and LSR. Here, the bufferregion BFR may be formed to have a width greater than the pad regions.For example, the width of the buffer region BFR may be 3 to 150 timesthe width of each of the pad regions.

In some example embodiments, a thickness of the buffer region BFR may besmaller than or equal to the minimum thickness of the upper staircaseregion USR and may be greater than or equal to the maximum thickness ofthe lower staircase region LSR. For example, the buffer region BFR maybe substantially coplanar with the lower staircase region LSR.

The three-dimensional semiconductor device may further include theinsulating layer 120 covering the electrode structure 110. Theinsulating layer 120 may be provided to cover the whole top surface ofthe buffer region BFR, except for the contact plugs 130 penetrating theinsulating layer 120, and to have a substantially flat top surface. Forexample, any pattern made of the same material as the horizontalelectrodes may not be provided between the buffer region BFR and theinsulating layer 120. Accordingly, the insulating layer 120 may have amonotonically increasing thickness in a direction from the upperstaircase region USR toward the lower staircase region LSR. For example,the whole top surface of the buffer region BFR, except for the contactplugs 130 penetrating the insulating layer 120, may be in direct contactwith the insulating layer 120.

A thickness of each of the upper and lower staircase regions USR and LSRmay decrease several times in a stepwise manner in a direction away fromthe cell array region CAR. Each of the upper and lower staircase regionsUSR and LSR may have at least two different thicknesses, which arechanged in an alternating manner when measured at the same distance fromthe cell array region CAR.

When viewed in a plan view, the uppermost one of the horizontalelectrodes constituting the buffer region BFR may include a connectingportion CP continuously extending from the upper staircase region USR tothe lower staircase region LSR and a protruding portion PP horizontallyprotruding from the connecting portion CP. The protruding portion PP maybe spaced apart from one or both of the upper and lower staircaseregions USR and LSR. For example, the uppermost one of the horizontalelectrodes constituting the buffer region BFR may be formed to have a‘T’-shaped structure, when viewed in a plan view.

FIG. 12B corresponds to FIG. 12A, but uses conventional staircaseterminology. As shown in FIG. 12B, at least one of the conductive treadsT includes multiple levels. Moreover, a plurality of conductive vias Vare provided, a respective one of which electrically contacts arespective one of the conductive treads T and extends away from therespective one of the conductive treads T. An insulating layer I is alsoprovided on the staircase SC. The insulating layer I includes a flatouter surface on the steps S and a flat outer surface on theintermediate landing IL. As also shown, the insulating layer I increasesin thickness going down the steps S of the staircase SC.

FIGS. 13 and 14 are perspective views illustrating a method of forming astaircase-shaped connection structure according to other exampleembodiments of the inventive concepts. For concise description, anelement previously described with reference to FIGS. 1 through 12 may beidentified by a similar or identical reference number without repeatingan overlapping description thereof.

Referring to FIGS. 7 and 13, a photolithography process may be performedon the third mask layer ML to form the third mask pattern M3 withopenings OP. The openings OP may be formed to partially expose the upperand lower staircase structures USS and LSS. In the present embodiments,the formation of the third mask pattern M3 may include one exposure stepand one developing step, which may be performed on the third mask layerML. Each of the openings OP may be formed across the buffer region BFRand expose both of the upper and lower staircase structures USS and LSS.

Next, the horizontal layers 114 exposed by the openings OP may be etchedby a third etching step using the third mask pattern M3 as an etch mask.With regard to an etch depth, the third etching step may be performedusing the single-layer etching method. For example, the etch depth ofthe third etching step may be substantially equal to or smaller than thevertical pitch of each of the horizontal layers 114. Accordingly, atleast one single-level stair may be formed in each of the multi-levelstairs constituting the upper and lower staircase structures USS andLSS. Since each of the openings OP is formed across the buffer regionBFR, the single-level stair may be formed not only on the upper andlower staircase structures USS and LSS but also on the buffer regionBFR, as shown in FIG. 14.

Referring to FIG. 14, when viewed in a plan view, the uppermost one ofthe horizontal electrodes constituting the buffer region BFR maycontinuously extend from the upper staircase region USR to the lowerstaircase region LSR and continuously expose the second uppermost one ofthe horizontal electrodes from the upper staircase region USR to thelower staircase region LSR. For example, the uppermost one of thehorizontal electrodes constituting the buffer region BFR may have a barshape.

FIG. 15 is a sectional view illustrating a coated profile of aphotoresist layer according to a comparative example, and FIG. 16 is agraph showing a change in thickness of a photoresist layer with respectto position in the comparative example.

According to the comparative example, as shown in FIGS. 15 and 16, thebuffer region BFR may not be formed between the upper and lowerstaircase regions USR and LSR, and thus, the upper and lower staircaseregions USR and LSR may be formed adjacent to each other. In this case,as shown in FIG. 16, the third mask layer ML may have an increasingthickness in a direction from the cell array region CAR toward the lowerstaircase region LSR (for example, T1<T2<T3<T4). Accordingly, in thecase where the number of layers constituting the stack 110 increases,the third mask layer ML may have an increased thickness variation ΔT1between the upper and lower staircase regions USR and LSR.

Since an exposure step can only be effectively performed within aspecific range of focal length, the increase in thickness variation ΔT1of the third mask layer ML makes it difficult to expose effectively bothof the upper and lower staircase regions USR and LSR through a singleexposure step. In other words, in the case where the buffer region BFRis absent, the thickness variation ΔT1 may be too large to effectivelyexpose the third mask layer ML through one exposure step. Furthermore,in the case where the buffer region BFR is absent, the thicknessvariation ΔT1 of the third mask layer ML may be excessive. In this case,the photolithography process may not be effectively performed on thethird mask layer ML.

FIG. 17 is a sectional view illustrating a coated profile of aphotoresist layer according to example embodiments of the inventiveconcepts, and FIG. 18 is a graph showing a change in thickness of aphotoresist layer with respect to position example embodiments of theinventive concepts. FIG. 19 is a sectional view illustrating a coatedprofile of a photoresist layer according to other example embodiments ofthe inventive concepts, and FIG. 20 is a graph showing a change inthickness of a photoresist layer with respect to position according toother example embodiments of the inventive concepts.

According to example embodiments of the inventive concepts, the bufferregion BFR may be provided between the upper and lower staircase regionsUSR and LSR. Accordingly, when compared with the case of the absence ofthe buffer region BFR, the third mask layer ML may have a reducedthickness variation ΔT2 (i.e., ΔT2<ΔT1), as shown in FIGS. 17 and 18 ora substantially uniform thickness (i.e., ΔT3˜0), as shown in FIGS. 19and 20. In other words, the presence of the buffer region BFR makes itpossible to improve uniformity in thickness of the third mask layer ML.Accordingly, as described with reference to FIGS. 13 and 14, theopenings OP may be formed at once by one exposure step and onedeveloping step to cross both of the upper and lower staircase regionsUSR and LSR.

Alternatively, as described with reference to FIGS. 1 through 12, theopenings OP may be formed by two exposure steps and one developing stepto expose the upper and lower staircase regions USR and LSR,respectively. Especially, as shown in FIG. 9, in the case that there isthe buffer region BFR, some of the openings OP exposing the upperstaircase regions USR may be formed spaced apart from the others of theopenings OP exposing the lower staircase regions LSR. In other words,the two exposure steps may be performed in such a way that regionsexposed thereby are not overlapped with each other.

By contrast, if the buffer region BFR is not provided as described inthe comparative example of FIG. 15, in order to apply the single-layeretching method to all of the multi-level stairs constituting the stack110, at least two exposure steps should be performed in such a way thatregions exposed thereby are overlapped with each other in at least oneportion. However, such an overlap between the exposed regions may leadto technological problems such as an over-dose problem, and this makesit difficult to realize a desired shape of the opening OP.

FIG. 21 is a circuit diagram illustrating a three-dimensionalsemiconductor memory device according to example embodiments of theinventive concepts.

Referring to FIG. 21, a three-dimensional semiconductor memory devicemay include a common source line CSL, a plurality of bit lines BL0, BL1,and BL2, and a plurality of cell strings CSTR disposed between thecommon source line CSL and the bit lines BL0-BL2.

The common source line CSL may be a conductive pattern provided on thesubstrate 10 or a doped region provided in the substrate 100. The bitlines BL0-BL2 may be conductive patterns (for example, metal lines)provided over the substrate 100. The bit lines BL0-BL2 may be spacedapart from and parallel to each other, and a plurality of cell stringsCSTR may be connected in parallel to each of the bit lines BL0-BL2.Accordingly, the cell strings CSTR may also be two-dimensionallyprovided on the common source line CSL or the substrate 100.

Each of the cell strings CSTR may include a ground selection transistorGST coupled to the common source line CSL, a string selection transistorSST coupled to one of the bit lines BL0-BL2, and a plurality of memorycell transistors MCT disposed between the ground and string selectiontransistors GST and SST. The ground selection transistor GST, the stringselection transistor SST, and the memory cell transistors MCT may beconnected in series to each other. Furthermore, a ground selection lineGSL, a plurality of word lines WL0-WL3 and a plurality of stringselection lines SSL0-SSL2 may be provided between the common source lineCSL and the bit lines BL0-BL2 to serve as gate electrodes of the groundselection transistor GST, the memory cell transistors MCT, and thestring selection transistors SST, respectively.

The ground selection transistors GST may be disposed at thesubstantially same level (for example, relative to the substrate 100),and the gate electrodes thereof may be connected in common to the groundselection line GSL, thereby being in an equipotential state. Similarly,the gate electrodes of the memory cell transistors MCT located at thesame level may be connected in common to one of the word lines WL0-WL3,thereby being in an equipotential state. Since each of the cell stringsCSTR includes a plurality of the memory cell transistors MCT disposed atdifferent levels from each other, the word lines WL0-WL3 may have amulti-layered structure between the common source line CSL and the bitlines BL0-BL2. The word lines WL0-WL3 of the multi-layered structure maybe configured to have substantially the same technical features as thoseof the semiconductor devices previously described with reference to FIG.12A and FIG. 14.

Each of the cell strings CSTR may include a semiconductor patternvertically extending from the common source line CSL to be connected toone of the bit line BL0-BL3. A memory layer or a memory element may beprovided between the word lines WL0-WL3 and the semiconductor pattern.In example embodiments, the memory layer or the memory element mayinclude a material or a layer structure, in which electric charges canbe selectively stored. For example, the memory layer may include aninsulating layer with many trap sites (e.g., a silicon nitride layer), afloating gate electrode, and/or an insulating layer provided withconductive nano dots.

For example, each of the cell strings CSTR may include horizontalpatterns HP, which are vertically separated from each other by theinterlayered insulating layers 112, and vertical patterns VP, which areprovided to penetrate the horizontal patterns HP. The vertical patternsVP and the horizontal patterns HP may be formed to have one of severalstructures illustrated in FIGS. 22 through 25. In the case of theembodiments previously described with reference to FIGS. 1 through 14,the horizontal patterns HP may be the horizontal layers 114.Alternatively, the horizontal patterns HP may be provided as theresulting structure of the replacement process performed on thehorizontal layers 114. Accordingly, the horizontal patterns HP may beconfigured to have the same features as the staircase-shaped structureshown in FIGS. 12 and 14.

Referring to FIGS. 22 through 25, the vertical pattern VP may include asemiconductor pattern SP serving as a channel region, and the horizontalpattern HP may include a horizontal electrode HE serving as a gateelectrode. In example embodiments, the vertical pattern VP may furtherinclude a vertical insulating layer VI that is inserted into thesemiconductor pattern SP. Furthermore, each of the memory celltransistors MCT may further include a tunnel insulating layer TL, acharge storing layer CL, and a blocking insulating layer BK thatconstitute a memory element.

In example embodiments, as shown in FIG. 22, the tunnel insulating layerTL, the charge storing layer CL, and the blocking insulating layer BKmay constitute the vertical pattern VP. In other embodiments, as shownin FIG. 25, the tunnel insulating layer TL, the charge storing layer CL,and the blocking insulating layer BK may constitute the horizontalpattern HP. In other embodiments, as shown in FIG. 23, the tunnelinsulating layer TL and the charge storing layer CL may constitute thevertical pattern VP, and the blocking insulating layer BK may constitutethe horizontal pattern HP. In still other embodiments, as shown in FIG.24, the tunnel insulating layer TL may constitute the vertical patternVP, and the charge storing layer CL and the blocking insulating layer BKmay constitute the horizontal pattern HP. However, example embodimentsof the inventive concepts will not be limited to the examples shown inFIGS. 22 through 25. For example, at least one of the tunnel insulatinglayer TL, the charge storing layer CL, and the blocking insulating layerBK may be provided in a multi-layered structure. Furthermore, themulti-layered structure may be configured to include layers, at leastone of which is included in the vertical pattern VP and the other ofwhich is included in the horizontal pattern HP.

The charge storing layer CL may be an insulating layer with many trapsites and/or an insulating layer with nano particles and may be formedby a chemical vapor deposition and/or atomic layer deposition process.For example, the charge storing layer CL may include a trap insulatinglayer, a floating gate electrode, and/or an insulating layer withconductive nano dots. In example embodiments, the charge storing layerCL may include a silicon nitride layer, a silicon oxynitride layer, asilicon-rich nitride layer, a nanocrystalline silicon layer, and/or alaminated trap layer.

The tunnel insulating layer TL may be one or more materials having agreater band gap than the charge storing layer CL and be formed by achemical vapor deposition and/or atomic layer deposition process. Forexample, the tunnel insulating layer TL may be a silicon oxide layer,which may be formed using one of the above deposition techniques.Furthermore, a thermal treatment process may be further performed on thetunnel insulating layer TL, for example, after the deposition thereof.The thermal treatment may be a rapid thermal nitridation (RTN) processand/or an annealing process to be performed under atmosphere containingat least one of nitrogen and oxygen.

The blocking insulating layer BK may include the first and secondblocking insulating layers that are formed of different materials fromeach other. In example embodiments, one of the first and second blockinginsulating layers may be configured to have a band gap that is smallerthan that of the tunnel insulating layer TL and higher than that of thecharge storing layer CL. Further, the first and second blockinginsulating layers may be formed using a chemical vapor deposition and/oran atomic layer deposition, and one of them may be formed by a wetoxidation process. In example embodiments, the first blocking insulatinglayer may include a high-k dielectric, such as aluminum oxide and/orhafnium oxide, and the second blocking insulating layer may be amaterial, whose dielectric constant is smaller than the first blockinginsulating layer. In other embodiments, the second blocking insulatinglayer may be one or more high-k dielectrics, and the first blockinginsulating layer may be a material, whose dielectric constant is smallerthan the second blocking insulating layer.

FIG. 26 is a circuit diagram illustrating a three-dimensionalsemiconductor memory device according to other example embodiments ofthe inventive concepts.

Referring to FIG. 26, a plurality of selection transistors SST may beconnected in parallel to a bit line BL via a plurality of bit line plugsBLP. Each of the bit line plugs BLP may be connected in common to a pairof the selection transistors SST disposed adjacent thereto.

A plurality of word lines WL and a plurality of vertical electrodes VEmay be provided between the bit line BL and the selection transistorsSST. The word lines WL may be configured to have substantially the sametechnical features as the semiconductor device exemplarily describedwith reference to FIGS. 12 and 14. The vertical electrodes VE may beprovided between the bit line plugs BLP. For example, the verticalelectrodes VE and the bit line plugs BLP may be alternatingly arrangedalong a direction parallel to the bit line BL. Furthermore, each of thevertical electrodes VE may be connected in common to a pair of theselection transistors SST disposed adjacent thereto.

A plurality of memory elements ME may be connected in parallel to eachof the vertical electrodes VE. Each of the memory elements ME may beconnected to the corresponding one of the word lines WL. In other words,each of the word lines WL may be connected to the corresponding one ofthe vertical electrodes VE via the corresponding one of the memoryelements ME.

Each of the selection transistors SST may include a selection line SLserving as a gate electrode thereof. In example embodiments, theselection lines SL may be parallel to the word lines WL.

Three-dimensional semiconductor memory devices according to exampleembodiments of the inventive concepts have been described with referenceto FIGS. 21 through 26. These are merely provided as examples, to whichthe inventive concepts can be applied, but example embodiments of theinventive concepts may not be limited thereto.

FIGS. 27 and 28 are schematic block diagrams illustrating electronicdevices including a semiconductor device according to exampleembodiments of the inventive concepts.

Referring to FIG. 27, an electronic device 1300 including asemiconductor device according to example embodiments of inventiveconcepts may be used in a personal digital assistant (PDA), a laptopcomputer, a mobile computer, a web tablet, a wireless phone, a cellphone, a digital music player, a wire or wireless electronic device,and/or a complex electronic device including at least two of thesedevices. The electronic device 1300 may include a controller 1310, aninput/output device 1320 such as a keypad, a keyboard, a display, amemory 1330, and a wireless interface 1340 that are combined to eachother through a bus 1350. The controller 1310 may include, for example,a microprocessor, a digital signal processor and/or a microcontroller orthe like. The memory 1330 may be configured to store a command code tobe used by the controller 1310 or a user data. The memory 1330, thewireless interface 1340, the I/O device 1320 and/or the controller 1310may include a semiconductor device according to example embodiments ofthe inventive concepts. The electronic device 1300 may use a wirelessinterface 1340 configured to transmit data to and/or receive data from awireless communication network using a RF signal. The wireless interface1340 may include, for example, an antenna, a wireless transceiver and soon. The electronic system 1300 may be used in a communication interfaceprotocol of a communication system such as CDMA, GSM, NADC, E-TDMA,WCDMA, CDMA2000, Wi-Fi, Muni Wi-Fi, Bluetooth, DECT, Wireless USB,Flash-OFDM, IEEE 802.20, GPRS, iBurst, WiBro, WiMAX, WiMAX-Advanced,UMTS-TDD, HSPA, EVDO, LTE-Advanced and/or MMDS, and so forth.

Referring to FIG. 28, a memory system including a semiconductor deviceaccording to example embodiments of inventive concepts will bedescribed. The memory system 1400 may include a memory device 1410 forstoring huge amounts of data and a memory controller 1420. The memorycontroller 1420 controls the memory device 1410 so as to read datastored in the memory device 1410 or to write data into the memory device1410 in response to a read/write request of a host 1430. The memorycontroller 1420 may include an address mapping table for mapping anaddress provided from the host 1430 (e.g., a mobile device or a computersystem) into a physical address of the memory device 1410. The memorydevice 1410, the memory controller 1420 and/or the host 1430 may includea semiconductor device according to example embodiments of inventiveconcepts.

The semiconductor memory devices disclosed above may be encapsulatedusing various and diverse packaging techniques. For example, thesemiconductor memory devices according to the aforementioned embodimentsmay be encapsulated using a package on package (POP) technique, a ballgrid arrays (BGAs) technique, a chip scale packages (CSPs) technique, aplastic leaded chip carrier (PLCC) technique, a plastic dual in-linepackage (PDIP) technique, a die in waffle pack technique, a die in waferform technique, a chip on board (COB) technique, a ceramic dual in-linepackage (CERDIP) technique, a plastic quad flat package (PQFP)technique, a thin quad flat package (TQFP) technique, a small outlinepackage (SOIC) technique, a shrink small outline package (S SOP)technique, a thin small outline package (TSOP) technique, a system inpackage (SIP) technique, a multi-chip package (MCP) technique, awafer-level fabricated package (WFP) technique and/or a wafer-levelprocessed stack package (WSP) technique.

The package in which a semiconductor memory device according to exampleembodiments may be mounted may further include at least onesemiconductor device (e.g., a controller and/or a logic device) that isconfigured to control the semiconductor memory device.

According to example embodiments of the inventive concepts, astaircase-shaped connection structure may be formed to have a bufferregion. The presence of the buffer region makes it possible to improveuniformity in thickness of a mask pattern, which may be used for asingle-layer etching step. Accordingly, the single-layer etching stepcan be performed with improved process reliability. In exampleembodiments, due to the improved uniformity in thickness of the maskpattern, the mask pattern can be formed by one exposure step, and thismakes it possible to simplify a process of fabricating a semiconductordevice.

While example embodiments of the inventive concepts have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: performing a first etch to form a first staircasestructure in a stack of alternating first and second layers, wherein afirst step in the first staircase structure comprises a first pluralityof the second layers; performing a second etch to form a secondstaircase structure in the stack, wherein a second step in the secondstaircase structure comprises a second plurality of the second layers;and performing a third etch to: reduce the first step in the firststaircase structure to a single one of the first plurality of the secondlayers; and reduce the second step in the second staircase structure toa single one of the second plurality of the second layers.
 2. The methodof claim 1, wherein the stack comprises a buffer region between thefirst staircase structure and the second staircase structure, whereinthe performing the second etch comprises forming the second staircasestructure to step down from the buffer region, and wherein the bufferregion comprises a planar uppermost surface that extends a longerdistance than the second step.
 3. The method of claim 2, wherein theperforming the third etch comprises forming the single one of the firstplurality of the second layers and the single one of the secondplurality of the second layers by etching to a depth equal to or smallerthan a vertical pitch of the second layers.
 4. The method of claim 1,wherein the performing the third etch to reduce the first step in thefirst staircase structure further comprises reducing the first step to afirst single one of the first layers, and wherein the performing thethird etch to reduce the second step in the second staircase structurefurther comprises reducing the second step to a second single one of thefirst layers.
 5. A method of forming a semiconductor device, the methodcomprising: performing a first etch of a stack of alternating first andsecond layers to form a first staircase structure comprising a firstplurality of multi-level steps that step up from a buffer region of thestack; then performing a second etch of the stack to form a secondstaircase structure comprising a second plurality of multi-level stepsthat step down from the buffer region; and performing a third etch onboth of the first and second staircase structures.
 6. The method ofclaim 5, wherein: one of the first plurality of multi-level stepscomprises a first plurality of the second layers in the first staircasestructure; one of the second plurality of multi-level steps comprises asecond plurality of the second layers in the second staircase structure;the one of the second plurality of multi-level steps protrudes a firstdistance from the stack in a direction; the buffer region comprises aplanar uppermost surface that extends a second distance, in thedirection, that is longer than the first distance; and the performingthe third etch comprises etching to a depth equal to or smaller than avertical pitch of the second layers to: reduce the one of the firstplurality of multi-level steps in the first staircase structure to asingle one of the first plurality of the second layers and a firstsingle one of the first layers; and reduce the one of the secondplurality of multi-level steps in the second staircase structure to asingle one of the second plurality of the second layers and a secondsingle one of the first layers.
 7. A method of forming a semiconductordevice, the method comprising: performing a first etch to form a firststaircase structure in a stack of alternating first and second layers,wherein a first step in the first staircase structure comprises a firstplurality of the second layers; performing a second etch to form asecond staircase structure in the stack, wherein a second step in thesecond staircase structure comprises a second plurality of the secondlayers, wherein the stack comprises a buffer region between the firststaircase structure and the second staircase structure, and wherein theperforming the second etch comprises forming the second staircasestructure to step down from the buffer region; and performing a thirdetch to: reduce the first step in the first staircase structure to asingle one of the first plurality of the second layers; and reduce thesecond step in the second staircase structure to a single one of thesecond plurality of the second layers.
 8. The method of claim 7, whereinthe buffer region comprises a planar uppermost surface that extends alonger distance than the second step.
 9. The method of claim 7, whereinthe performing the first etch comprises forming the first staircasestructure to step up from the buffer region.
 10. The method of claim 9,wherein the performing the first etch is performed before the performingsecond etch.
 11. The method of claim 1, wherein sidewalls of the firstplurality of the second layers in the first step are vertically aligned,and wherein sidewalls of the second plurality of the second layers inthe second step are vertically aligned.
 12. The method of claim 1,wherein the first staircase structure is formed in an upper portion ofthe stack and the second staircase structure is formed in a lowerportion of the stack.